1. Field of the Invention
This invention relates to a differential signal transmission cable property evaluating mechanism and a differential signal transmission cable property evaluating method.
2. Description of the Related Art
In several Gbit/s or more high speed digital signal processing devices such as servers, routers, storage products and the like, differential signaling is used for signal transmission between the devices, or between substrates (circuit boards) in the devices.
The differential signaling refers to transmitting 180 degrees-phase inverted signals in two paired signal line conductors respectively, and combining and outputting the differential signals received in a receiver. Electrical currents flowing in the one pair of the signal line conductors respectively flow in opposite directions to each other, and electromagnetic waves radiated from the transmission lines are therefore small. Also, extrinsic noise is superimposed equally on the one pair of the signal line conductors, and the effect of the noise is therefore canceled out by the receiver combining and outputting the differential signals. For these reasons, the differential signaling is often used for high speed digital signal transmission.
As a differential signal transmission cable used for the differential signaling, there has been one having one pair of signal line conductors, an insulator for covering respective circumferences of the one pair of the signal line conductors together, a shield conductor provided around a perimeter of the insulator, and a sheath provided around a perimeter of the shield conductor.
As a mechanism for evaluating a property of the differential signal transmission cable, there has been known a type which mounts two electrical length (phase) matched semi-rigid cables to the differential signal transmission cable, but no mechanism or method for evaluating the property of the differential signal transmission cable has firmly been established.
Refer to JP-A-2008-108475, for example.